GB604131A - Receiver-transmitting arrangement for carrier-frequency wave signals - Google Patents

Abstract

604,131. Radio-signalling. HAZELTINE CORPORATION. Jan. 16, 1945, No. 1349. Convention date, Feb. 11, 1944. [Class 40 (v)] A receiver-transmitter arrangement comprises a regenerative oscillatory circuit including a valve, having an anode-cathode circuit to which a periodic quench voltage is applied to enable the arrangement to be used as a super-regenerative receiver, a circuit to derive an output signal representing the modulation of the received wave, and means for applying a modulating potential to the anode-cathode circuit of the valve to enable the arrangement to transmit a modulated carrier signal. The arrangement is specially applicable to radio beacons for emitting an identification or other signal in response to a received interrogating signal. A resonant circuit, Fig. 1, comprising a variable inductance 11, which is connected to control grid of a valve 10, and a condenser C, which may be comprised wholly or partly by the self capacity of coil 11 and the anodegrid capacity of valve 10, is coupled to the anode of valve 10 by a condenser 12. The mid-point of coil 11 is grounded through a radio-frequency choke 13, and the cathode of valve 10 is earthed through R.F. choke 14, and a bias resistor-condenser combination 15, 16. Oscillator 20 produces a periodic quench voltage which is applied to valve 10 through an amplifier 21 and a cathode-follower 22, cathode load 23 of which is coupled to the anode of valve 10 by condenser 24 and. R.F. choke 25, thus enabling the arrangement to act as a superregenerative receiver. A diode detector 30 is coupled to the oscillatory circuit by condenser 31, and has as a.load an R.F. choke 32 and a resistance 33. The output of a pulse-modulated generator 50, which is triggered by the output of detector 30, is applied to the anode of valve 10 through an amplifier 51, a pulsetransformer 52, a quench-frequency filter circuit 53 and R.F. choke 25. A single aerial system 60, is used for both receiving and transmitting. When no signal is being received, a low-amplitude signal voltage having components of the quench frequency and its harmonics as well as components corresponding to the noise signals of the regenerative circuit appears across resistance 33. A portion of this signal, such as the quench-frequency component is utilized in a unit 40, comprising an amplifier and rectifier, to produce a negative control voltage which is applied to amplifier 21, and controls the characteristics of the arrangement during reception as described in Specification 592,271. The detected signal is also applied to the generator 50, but is of too low an amplitude to trigger it, so that the receiver operation continues. If a pulsemodulated interrogating signal is received, the output of detector 30 contains both high amplitude and low amplitude components, but the pulse repetition frequency of the received signal is usually such that the operation of the unit 40 remains unaltered. The detected signal is also applied to generator 50, which in response to the first high amplitude component, applies a single positive pulse to the anode of valve 10, for a time determined by the circuit of generator 50. The applied pulse, which is of substantially greater magnitude than the quench voltage, causes the valve 10 and the regenerative circuit to transmit a single R.F. pulse of duration corresponding to the applied pulse, and at a frequency which is higher than that of the received R.F. signal. At the trailing edge of each applied positive pulse, the quench voltage again becomes effective to enable the apparatus to operate as a receiver. The operating frequency during reception depends on the parameters of the resonant circuit and the electron transit time of valve 10. If the transit time of valve 10 were neglected the operating frequency would be the resonant frequency fo, Fig. 2, of the resonant circuit, which has a phase-shift frequency characteristic as shown. The transit-time of the valve may not be neglected at the ultra-high frequency range, and imparts a lagging phase to the voltage appearing across the resonant circuit, and the oscillatory circuit operates at a frequency such that it imparts a compensating leading phase to the voltage. Since the quench voltage applied to valve 10 may be relatively low amplitude for linear operation of the arrangement of Fig. 1 asa receiver, the transit time may be a substantial part of the period of oscillation, so that the -operating frequency f r is considerably lower than the resonant frequency of the circuit C, 11. During operation as a transmitter a substantially greater voltage is applied to the anode of valve 10, thus reducing the electron transit time, and causing the circuit to oscillate at a higher frequency ft, Fig. 2. Quench-frequency oscillator 20 may generate a rectangular or a sinusoidal wave-form. The time-constants of generator 50 may be such that the transmitted pulse has the same or a different duration and repetition frequency as the .interrogating signal. In a modification, Fig. 3 (not shown), the quench-voltage is cut off during intervals of transmission. The portion 70 of the circuit of Fig. 1 is replaced by an arrangement in which the cathode of cathode-follower 22 is earthed through filter circuit 53 and the secondary of transformer 52. During intervals of transmission, the cathode of valve 22 is driven positive, thus blocking the supply circuit for the quench-voltage. The generator 50 may be isolated from the output circuit of detector 30, and a switch inserted in the arrangement so that it may be used as a receiver or transmitter.